1. Field of the Invention
The present invention relates to a monolithic antenna, and more particularly to a monolithic microwave/milliwave antenna used in signal circuits, such as amplifiers, frequency converters, oscillators, transmitters and modulators, which have been combined in a single unit with an antenna for inputting and outputting microwave/milliwave band signals.
2. Description of the Related Arts
In general, antennas for inputting and outputting microwave/milliwave band signals have small dimensions, due to the shorter wavelength of the waves transmitted. Therefore, it is possible to construct a front end in which an antenna and a signal circuit, such as a transmit/receive circuit or the like, are combined in a single monolithic structure on, for instance, a semiconductor substrate such as gallium arsenide (GaAs). As a conventional example of such a configuration, a monolithic phased array antenna has been proposed. (For reference see for instance: J. F. Millvenna: "Monolithic Phased Arrays for EHF-Communications Terminals", Microwave Journal, pp.113-125, March 1988, D. M. Pozar et al: "Comparison of Architecture for Monolithic Phased Array Antennas", Microwave Journal, pp.93-104, March 1986, and R. J Mailloux: "Phased Array Architectures for mm-Wave Active Arrays", Microwave Journal, pp.117-120 July 1996).
In the conventional examples, in which this type of monolithic antenna is combined in a single unit with an RF circuit or an active element or the like, an antenna element and a feeding circuit are formed on a planar surface.
FIG. 9 is a perspective view of an example of a conventional monolithic microwave/milliwave dipole antenna.
As shown in the diagram, an active element circuit 13 and a stripline dipole antenna 12 are provided on the upper surface of a substrate14. In addition, a grounding conductor 15 is provided on another surface of the substrate 14.
In this configuration, the antenna resonates for electromagnetic waves having a wavelength equal to half the electrical length of the antenna and radiates the electromagnetic waves into space. In this case, the wavelength compression rate is 1/(.epsilon.r).sup.1/2. If we assume that .epsilon.r=12.7 in the case when the substrate comprises GaAs, the compression rate will be 0.28. At 60 GHz, antenna length will be 0.7 mm.
Furthermore, FIG. 10 is a perspective view of an example of a conventional microwave/milliwave patch antenna.
Here, an active element circuit 13 and a stripline patch antenna 16 are disposed on the upper surface of a substrate 14 in a similar configuration to the example shown in FIG. 9. In addition, a grounding conductor 15 is provided on another surface of the substrate 14.
In this patch antenna, the distance from the input or output terminal to the opposite terminal is equivalent to half the wavelength of an electromagnetic wave. Since a certain amount of area is therefore required, the dipole antenna is superior from the point of view of area utilized. However, at 60 GHz, the half-wavelength of an electromagnetic wave in free space is 2.5 mm, which is greater than the 0.7 mm in the dipole example described above. As a consequence, the stripline antenna has the disadvantages that energy cannot be effectively radiated and therefore sufficient gain cannot be obtained. Furthermore, when the antenna is provided on a flat surface together with a feeding circuit, an active circuit or the like, the properties of the antenna are liable to deteriorate due to the protective resin for protecting the surface of the antenna when it is mounted in a package.
Furthermore, as a known example of an antenna similar to the above, FIGS. 11A and 11B show a perspective view and cross-sectional view of a conventional microwave/milliwave horn antenna array. (For reference, see for instance: Schwering: "Millimeter Wave Antennas", Proceedings of the IEEE, vol.80, No.1, January 1992)
This horn antenna array comprises antennas 20 provided in an array within a single plane. Each of the antennas 20 comprises an antenna element 21 and a pyramid-shaped horn 22. Furthermore, silicon wafers are separated into upper surface wafers 23 and underside wafers 24, with the antenna elements 21 sandwiched therebetween. The antenna elements 21 are held on the opening side by the vertexes of the pyramid horns 22.
However, in this configuration, the operation of etching in the semiconductor substrate in order to form the vertex side quadrangular pyramids is difficult. The above document refers to an example in which an Si &lt;111&gt; surface was used, but even when etching is performed on a wafer (100) surface of GaAs used as an MMIC (Monolithic Microwave Integrated Circuit) substrate, it is not possible to achieve a precise pyramid shape. An improved etching method is therefore needed to achieve this configuration.
Furthermore, FIG. 12 shows a configuration of a conventional single-unit antenna semiconductor device (for instance, as disclosed in Japanese Patent Application Laid-Open No. 7-74285 (1995)).
In this conventional example, a pellet 31, which has a circuit portion 31a, including such as a transistor, and a patch antenna 3b, is positioned facedown above a conductor 35 on a silicon substrate 32 and is connected thereto by bumps 33. The substrate 32 has a tapered horn to which a conductor 36 is provided. In addition, a conductor 34 for reflecting waves is provided to the underside of the pellet 31.
However, since this configuration is not monolithic, the overall dimensions are increased by an amount equal to the portion which cannot be provided monolithically. Moreover, a size of its package is increased with a consequent increase in cost-efficiency. Furthermore, since the semiconductor chip (pellet 31) must be manufactured separately from the antenna portion (substrate 32), this configuration is not cost efficient to assemble.